Hydrogen Generator

ABSTRACT

A hydrogen generator includes a solid hydrogen source.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims priority toU.S. Ser. No. 10/640,567, filed on Aug. 14, 2003, which is herebyincorporated by reference.

TECHNICAL FIELD

This invention relates to a hydrogen generator.

BACKGROUND

An electrochemical cell is a device capable of providing electricalenergy from an electrochemical reaction, typically between two or morereactants. Generally, an electrochemical cell includes two electrodes,called an anode and a cathode, and an electrolyte disposed between theelectrodes. In order to prevent direct reaction of the active materialof the anode and the active material of the cathode, the electrodes areelectrically isolated from each other by a separator.

In one type of electrochemical cell, sometimes called a hydrogen fuelcell, the anode reactant is hydrogen gas, and the cathode reactant isoxygen (e.g., from air). At the anode, oxidation of hydrogen producesprotons and electrons. The protons flow from the anode, through theelectrolyte, and to the cathode. The electrons flow from the anode tothe cathode through an external electrical conductor, which can provideelectricity to drive a load. At the cathode, the protons and theelectrons react with oxygen to form water. The hydrogen can be generatedfrom a hydrogen storage alloy, by ignition of a hydride, or byhydrolysis of a liquid solution or slurry of a hydride.

SUMMARY

In one aspect, a hydrogen generator includes a housing, a solid hydrogensource disposed within the housing, and an inlet configured to guide afluid to contact the solid hydrogen source. The inlet can contact awicking region. The wicking region can include a wicking material thathas an affinity for the fluid. The wicking material can include ahydrophilic material. The housing can include a hydrogen gas outlet. Thehydrogen generator can include an end cap at one end of the housingincluding the inlet and the hydrogen gas outlet. The hydrogen gas outletcan include a gas permeable membrane. The inlet can be fluidly connectedto a fluid control system configured to control fluid flow rate to thesolid hydrogen source. The generator can be portable.

In another aspect, a method of generating hydrogen includes contacting afluid including a proton source and a solid hydrogen source disposedwithin a housing having an outlet configured to deliver the hydrogen toa hydrogen fuel cell. The fluid and the solid hydrogen source can becontacted by introducing the fluid into a hydrogen generator. Thehydrogen generator can include the housing. The solid hydrogen sourceand an inlet can be configured to guide the fluid to contact the solidhydrogen source. The method can include dissolving a catalyst in thefluid. In certain circumstances, the method can include passing thefluid through the inlet to a wicking material. The method can alsoinclude controlling the amount of fluid reaching the solid hydrogensource, for example, by determining an amount of hydrogen exitinggenerator. The fluid can include water or another proton source, whichcan be delivered as water vapor to the solid hydrogen source.

In another aspect, a method of manufacturing a hydrogen generatorincludes placing a solid hydrogen source in a housing, the housingincluding an inlet configured to guide a fluid to contact the solidhydrogen source. The method can include forming a housing insert fromthe solid hydride, for example, by combining the solid hydride with awicking material. The solid hydride can be combined with the wickingmaterial by constructing a wicking region from the wicking material anda region of the solid hydride. The wicking region can be constructed byforming a channel of the wicking material through the region of thesolid hydride or by forming a layer adjacent to the region of the solidhydride, for example, by rolling the layer adjacent to the region of thesolid hydride to form a layered roll. The channel can extend along along axis of the housing, along a radial axis of the housing, orcombinations thereof. In certain circumstances, the wicking material canbe combined with a catalyst. The method can also include placing an endcap in contact with the solid hydrogen source, the end cap including theinlet and a hydrogen gas outlet. The inlet can be fluidly connected to afluid control system configured to control fluid flow rate to the solidhydrogen source.

The solid hydrogen source can include a wicking region, for example, ofa wicking material such as a hydrophilic material, and a region of asolid hydride. The wicking region can form a layer adjacent to theregion of the solid hydride. For example, the wicking region and theregion of the solid hydride form a layered roll. The wicking region canbe a channel through the region of the solid hydride, which can extendalong a long axis of the housing, along a radial axis of the housing, oralong both dimensions of the housing. For example, the housing can becylindrical and the channel can extend along the length of the cylinder.

The solid hydrogen source can include a solid hydride, such as a hydridesalt, including an alkali or alkaline earth hydride, an aluminumhydride, or a borohydride. The borohydride can be lithium borohydride,sodium borohydride, potassium borohydride, or mixtures thereof. Thesolid hydride can be a pellet, tablet, cylinder, layer, or tube. Thesolid hydride can be combined with a wicking material. For example, thesolid hydrogen source can be a blend of the wicking material with thesolid hydride. The wicking material can include a catalyst. The fluidcan include a proton source capable of reacting within the solidhydrogen source to form hydrogen gas. For example, the proton source caninclude water.

Embodiments of a hydrogen generator can include one or more of thefollowing advantages. The hydrogen generator can have competitivevolumetric and gravimetric capacities relative to other hydrogensources. For example, a solid hydrogen source increases the volumetricenergy density of the generator in comparison to devices based onslurries or solutions of similar materials. The design of wickingregions in the solid hydrogen source can lead to more completeconversion of the materials contained within the generator to hydrogengas. The hydrogen generator can provide fuel to a fuel cell safely andreliably, and in a controllable manner. The addition of a catalystthroughout the solid hydrogen can control or modulate hydrogengeneration throughout the generator, which can decrease the overallrunning temperature of the generator, and improve safety factors. Thecomponents of the hydrogen generator can be relatively inexpensive,compared to the components of other hydrogen sources. The hydrogengenerator can be an economical, compact, portable, and/or disposablesource of hydrogen gas. The hydrogen generator based on a solid hydridecan be of a low weight relative to hydrogen sources employing reversiblemetal hydride alloys.

Electrochemical cell performance can be improved as well. In particular,solid sodium borohydride to which twice the stoichiometric amount ofwater was added, has been calculated to yield over a 50% improvement inruntime when compared to lithium ion rechargeable batteries for poweringportable consumer electronic devices, using practical numbers for fuelcell system components for such applications. In addition, the optimalsolid hydride utilization can be balanced with minimal volume allottedfor water infusion and hydrogen recovery, which can be adjusted ormodified by the placement of various hydrophobic and wicking materialsthroughout a solid hydride matrix. This can allow improved utilizationof reactants and improved control of hydrogen generation rate.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of an electrochemical cell.

FIG. 2A is a perspective view of solid hydrogen source.

FIG. 2B is a top view of a solid hydrogen source.

FIGS. 3A and 3C are perspective views of various solid hydrogen sources.

FIGS. 3B and 3D-F are top views of various solid hydrogen sources.

FIG. 4A is a perspective view of solid hydrogen source.

FIG. 4B is a side view of a solid hydrogen source in a housing.

FIG. 5 is a top view of a layered solid hydrogen source.

FIG. 6A is a side view of an end cap.

FIG. 6B is a top view of an end cap.

FIG. 6C is an end view of an end cap and solid hydrogen source.

FIGS. 7A-C are schematic representations of fluid control systems.

FIGS. 8A-C are schematic representations of fluid control systems.

DETAILED DESCRIPTION

Referring to FIG. 1, an electrochemical system 10 includes a hydrogengenerator 12 includes a housing 14 defining an internal volume 16.Disposed within the internal volume of the hydrogen generator is a solidhydrogen source 18. An inlet 20 is configured to guide a fluid, which isin fluid container 22, to contact the solid hydrogen source 18. Theinlet 20 can contact a wicking region 24, for example, of a hydrophilicmaterial, that can be included in the solid hydrogen source 18. Thehousing 12 can include a hydrogen gas outlet 26, which can be configuredto deliver the hydrogen to a hydrogen fuel cell.

Hydrogen gas outlet 26 of housing 14 can include a gas permeablemembrane. The membrane can contain any liquid component that couldpotentially exit through the outlet, thereby helping to limit or preventfluid leakage from the housing. The gas permeable membrane allows gas,particularly hydrogen gas, to exit the housing unimpeded whilepreventing solid particles from exiting the hydrogen generation housingby filtration. The gas permeable membrane can include a polymer, such asa poly(alkane), poly(styrene), poly(methacrylate), poly(nitrile),poly(vinyl), fluoropolymer, poly(diene), poly(xylylene), poly(oxide),poly(ester), poly(carbonate), poly(siloxane), poly(imide), poly(amide),poly(urethane), poly(sulfone), poly(aryl ether ether ketone), orcellulose, or a porous materials, such as a fiber or mineralsufficiently hydrophobic and microporous to restrict liquid, yet permithydrogen permeation, or combinations thereof. Combinations suitable toform a gas permeable membrane include co-polymers, polymer blends, andcomposites including inorganic-organic composites. Although housing 14in FIG. 1 has only one hydrogen gas outlet, in some cases the housinghas more than one hydrogen gas outlet yet allow unimpeded exit ofdesired hydrogen gas. To obtain adequate permeation rates, high surfacearea configurations of the gas permeable membrane, for example, parallelmicro-tubes, channels or layers, can be used. The gas permeablemembrane(s) can be placed at the outlet 26 of the generator orintegrated within the generator.

The hydrogen generator 12 can include an end cap 30 at one end of thehousing. End cap 30 includes the inlet 20. In certain embodiments, theend cap 30 includes the hydrogen gas outlet (not shown in FIG. 1). Thehydrogen gas outlet can include a gas permeable membrane. Gas permeablehydrophobic material can also be used as a pathway for moist gaseoushydrogen out of the cell.

Housing 14 can be a cylindrical housing. The housing can be made of ametal such as nickel or nickel plated steel, stainless steel, oraluminum-clad stainless steel, or a plastic such as polycarbonate,polyvinyl chloride, polypropylene, a polysulfone, ABS or a polyamide.The housing can have a length of between 1 cm and 30 cm, and a width ordiameter of between 1 cm and 20 cm. The housing can have a volume ofbetween 1 cm³ and 9,400 cm³.

The solid hydrogen source can include a solid hydride, such as an alkalior alkaline earth hydride, an aluminum hydride, or a borohydride. Theborohydride can be lithium borohydride, sodium borohydride, potassiumborohydride, or mixtures thereof. The solid hydride can be a pellet,tablet, cylinder, layer, or tube. In some cases, the solid hydrogensource can include an oxidizable material, such as a metal (e.g., zinc,aluminum, titanium, zirconium, or tin).

The fluid that is guided by the inlet can include a proton sourcecapable of reacting within the solid hydrogen source to generatehydrogen gas. For example, the proton source can include water and thesolid hydrogen source can include a solid hydride. A catalyst can beincluded in the fluid, or added to the fluid as it reacts within thesolid hydrogen source to facilitate generation of hydrogen gas. Ingeneral, hydrogen is generated by contacting the fluid and the solidhydrogen source. The fluid and the solid hydrogen source can becontacted by introducing the fluid into a hydrogen generator. The amountof fluid reaching the solid hydrogen source can be controlled, forexample, by determining an amount of hydrogen exiting generator.

The solid hydrogen source can include a binder. Examples of bindersinclude a polyethylene powder, a polypropylene, a polybutylene, a nylon,a polyacrylamide, a polyacrylate, a polyvinyl chloride, a polystyrene, apolymethylpentene, a Portland cement, or a fluorocarbon resin, such aspolyvinylidene fluoride or polytetrafluoroethylene. In certainembodiments, the binder can be a hydrophilic material, such as a fibrouspolymer fabric (e.g., polyvinyl alcohol fibers). The solid hydrogensource can include between 0.01% and 10% binder by weight.

The solid hydrogen source can include a wicking material, which can forma portion of the region 24. The wicking material can be a fibrouspolymer. The wicking material can include a hydrophilic material.Examples of a hydrophilic material include a nylon, a polyacrylamide, apolyacrylate, a polyvinyl chloride, a substituted polystyrene, or apolyvinyl alcohol. For example, the wicking material can includepolyvinyl alcohol fibers. The wicking material can include otheradditives. For example, the wicking material can include a surfactant(e.g., Triton X-100, available from Sigma-Aldrich). The surfactant canhelp to wet the wicking material, which can modify the rate of movementof the fluid through the wicking material.

The catalyst can be a component of the fluid or the catalyst can bedistributed on, dissolved in, or coated on the wicking material, inwhich case the catalyst can dissolve in the fluid as the fluid contactsor passes into the solid hydrogen source. The catalyst loading of thewicking material can be between 0.01% by weight and 5% by weight. Thecatalyst can include a transition metal salt, for example, a rutheniumor cobalt salt, or mixtures thereof. The catalyst can be a water solubletransition metal salt that activates the reaction of water with sodiumborohydride, such as cobalt(II) chloride and iron(II) chloride. Thecatalyst can either be stored in dry form within the solid hydrogensource matrix, as a dry metal or metal salt on an inert support (silica,alumina, zeolite, etc.) dispersed within the solid hydrogen sourcematrix, distributed within the solid hydrogen source configurationseparate from the solid hydrogen source matrix, or introduced as anaqueous solution. Soluble metal salts have high activity due to the highsurface area of the catalytic native metal particles produced uponreduction by sodium borohydride. Alternatively, the catalyst surface canbe a metal foil which can be co-laminated to the tape to be rolledwithin the wound cell configuration.

The combination of wicking material and solid hydride in the solidhydrogen source can form a wicking region of the wicking material and aregion of a solid hydride. The wicking material can guide or wick thefluid to the solid hydride, which can improve the overall yield ofhydrogen gas by more completely consuming the solid hydride in thegenerator. This can be accomplished by more completely distributing thefluid throughout the volume of the solid hydrogen source.

In one example, the wicking region can be incorporated into a channelthrough the region of the solid hydride, which can extend along a longaxis of the housing, along a radial axis of the housing, or along bothdimensions of the housing. Referring to FIG. 2A, a channel 70 (orplurality of channels which can be evenly distributed, as shown) canextend along the length of a cylindrical pellet 72 of a solid hydride ora blend of a solid hydride with a binder or additive. Referring to FIG.2B, a channel 74 can be a groove extending radially through acylindrical pellet 76, which can also extend along the length of thepellet. Referring to FIGS. 3A-F, tablets 80 can be stacked to form astructure such as a cylinder that is configured to fit within thehousing. Referring to FIGS. 3A and 3C, layers 82 of wicking material canbe interposed between tablets 80 so that the wicking region extendsradially with respect to the long axis of the structure. The tablets orpellets can be prepared by pressing a powder including the solidhydride. Referring to FIGS. 3A and 3B, a single channel 84 of wickingmaterial extends along the length of the structure. The channels can beprepared by drilling or otherwise forming lengthwise holes in thepellet. Referring to FIGS. 3C-3E, multiple channels 86, for example, 2to 8 channels, can be distributed around a tablets 80. Referring to FIG.3F, a channel layer 88 of wicking material can surround the periphery oftablets 80. Referring to FIGS. 3E and 3F, a design in which the wickingmaterial (channels 86 or channel layer 88) can allow void volume 90 tobe incorporated into the generator design between housing 14 and tablets80. The void volume 90 can be selected to accommodate the volumeexpansion that occurs to the pellet as hydrogen is generated.

By forming cylindrical pellets of solid hydride, it is possible tomaximize utilization of can volume to produce hydrogen. For example,solid hydride powder can be pressed into a pellet that has an actualdensity that is nearly theoretical density for the material (>98% of thetheoretical density of 1.074 g/cc for sodium borohydride. However,diffusion of water into and hydrogen out of a large dense pellet ofmaterial can be inefficient due to passivation of the hydride, bubblescaptured in the pellet and pockets of water blocking hydrogen flow. Thiscan be overcome by forming regions of hydrophilic and hydrophobicmaterials within or between the solid pellets. Wicking material can beused as a support for the catalyst. Fluid can then be wicked through thecatalyst to dissolve it and initiate reaction with the chemical hydride.The relative dimensions of the regions can be selected such that thediffusion length of fluid into the solid hydride can be minimized aswell as the volume that the wicking material displaces. Certainstructures can allow lateral diffusion and axial diffusion of fluidsimultaneously.

In another example, the region of the hydrophilic material can form alayer adjacent to the region of the solid hydride. Referring to FIG. 4A,cylindrical pellets 90 of a solid hydrogen source can be formed bypressing a powdered material, such as a solid hydride. Referring to FIG.4B, cylindrical pellets 90 can be stacked within a housing 14, and ahydrophilic material (not shown) can be introduced into the within oraround the stack of cylinders. Referring to FIG. 5, the wicking regionand the region of the solid hydride can form wicking layer 100 andhydride layer 102, which can be rolled to form a layered roll 104. Forexample, a layer of sodium borohydride can be dispersed as a powderrolled between hydrophilic/hydrophobic inert separators that would beused to direct water to the reactant to enable hydrogen generation. Asingle layer fuel tape can include sodium borohydride blended with ahydrophilic binder and an array of hydrophilic fibers. A tape made fromthis material can be made by a process akin to paper-making. The fueltape (paper) can be rolled with a hydrophobic membrane to separatelayers and allow for hydrogen to diffuse out. In such a system, catalystcan be dissolved in water, which could then be wicked into the roll fromone end, or the catalyst can be incorporated into the tape or theseparator layer.

More particularly, a tape consisting of the fuel/catalyst system can befabricated by making a mixture of powdered solid hydride, which can havea uniform mesh size, and a hydrophilic binder in a suitable solvent.Both the binder and solvent have to be unreactive toward the solidhydride. Examples of an binder include coathylene or isobutylene.Possible solvents include heavy hydrocarbons such as Isopar G. Thebinder should be less than 10% w/w of the solid hydride. The solidhydride/binder/solvent mixture can be blended and rolled into flatsheets using a roll coater such as a Rondo coater to form a sheet offuel tape. A separate sheet of hydrophilic cloth or wicking material canbe impregnated with a cobalt chloride solution and allowed to dry toform a catalyst sheet which can be calendared together with the fueltape to make the structure. By rolling under tension, this can make moreactive material available per unit volume. When the roll is placed in acylindrical housing and water can contact the wicking material which inturn dissolves the catalyst and initiates reaction with the fuel tape.Hydrogen diffuses through the holes covered with hydrophobic material inend caps positioned at the ends of the roll. The number of hydrogenoutlets and choice of membrane (based on hydrophobicity and gaspermeability) can be selected to maximize hydrogen generation rate.Hydrogen yields of up 85% or more can be achieved. By distributing thefluid, the heat generated by the solid hydrogen source can be controlledand maintained at or near ambient temperature.

When the fluid includes water, it can be delivered to the solid hydrogensource in a liquid phase or a gas phase. When delivered in a gas phase,this approach can permit water to be delivered more efficiently to thesolid hydrogen source predictably and reliably independent of geometricorientation of the device. For example, a small resistive heater can beincluded in generator that vaporizes liquid water in a reservoir priorto or while the water passes through the inlet. In another example, amembrane system can be utilized to enable controlled conversion ofliquid water to vapor-phase water that is then directed into the solidhydrogen source. After the hydrogen generation begins, the heatgenerated from the hydrogen generation can be utilized to provide heatto vaporize liquid water, allowing resistive heating to be needed at thebeginning of use.

End cap 30 can be designed to control the safety of the system andmaximize utilization of the solid hydrogen source by distributing thefluid throughout the solid hydrogen source. In particular, end cap 30can be designed to have a large contact area between the fluid and thesolid hydrogen source, which can minimize the diffusion length of thefluid into the solid hydrogen source, improving overall hydrogen yieldfrom the device. Referring to FIGS. 6A and 6B, end cap 30 includes theinlet 20 and hydrogen outlets 110. Hydrogen outlets 110 can bedistributed over the area of the cap to maximize surface contact withthe solid hydrogen source, which can facilitate collection of generatedgas. As discussed previously, a gas permeable membrane, such as ahydrophobic membrane, can cover the hydrogen outlets to contain solidsand liquids within the generator. Referring to FIG. 6C, end cap 30 canbe positioned over an end of solid hydrogen source 18, depicted here asa layered roll. Hydrogen outlets 110 are positioned over the end ofsolid hydrogen source 18 to facilitate collection of generated hydrogen.Inlet 20 contact wicks 112, which can be grooves or conduits of wickingmaterial on the contact side of cap 30. Wicks 112 can be patterned onthe cap to distribute water in a geometrical pattern that evenlydistributes the fluid as it is delivered to the solid hydrogen source.The wick can be patterned to minimize the radial arc lengths of fueltape between the wicks.

Referring to FIG. 1, an electrochemical system 10 the hydrogen gasoutlet 26 of hydrogen generator 12 is connected to a hydrogen fuel cell50. The fuel cell 50 has a housing 52 defining an internal volume 54.Within the internal volume are an anode 56 and a cathode 58, separatedby an electrolyte 60. The housing also has an oxygen or air inlet 62, anair and water outlet 64 through which oxygen-depleted air can alsoescape, and a hydrogen inlet 66. The hydrogen inlet 66 can be releasablyconnected to the hydrogen gas outlet 26 of the hydrogen generator 12.The connection between the hydrogen generator and the hydrogen fuel cellcan provide a conduit for hydrogen gas. Thus, hydrogen gas produced bythe hydrogen generator can travel to the fuel cell, where it can beconsumed by fuel cell anode 56. The connection between the hydrogengenerator and the fuel cell can be closed or opened as needed, using avalve or other means of regulating hydrogen flow to the fuel cell. Aconductor 68 can connect anode 56 and cathode 58 to drive a load whencurrent is produced.

In fuel cell 50, anode 56 oxidizes hydrogen gas to produce protons andelectrons. The protons move through electrolyte 60 to cathode 58, wherethe protons combine with oxygen, provided through oxygen or air inlet62, and electrons traveling through conductor 68 to produce water. Thewater can exit the fuel cell through air and water outlet 64. A feedbackcollection conduit (not shown) can collect water from the fuel cellcathode and feed the hydrogen generator. The anode 56 of the fuel cellcan be formed of a material capable of interacting with hydrogen gas toform protons and electrons. The material can be any material capable ofcatalyzing the dissociation and oxidation of hydrogen gas. Examples ofsuch materials include, for example, platinum or noble metals, platinumor noble metal alloys, such as platinum-ruthenium, and platinumdispersed on carbon black. Cathode 58 can be formed of a materialcapable of catalyzing the reaction between oxygen, electrons, andprotons to form water. Examples of such materials include, for example,platinum, platinum alloys, transition metals, transition metal oxides,and noble metals dispersed on carbon black. Electrolyte 60 is capable ofallowing ions to flow through it while also providing a substantialresistance to the flow of electrons. In some embodiments, electrolyte 60is a solid polymer (e.g., a solid polymer ion exchange membrane).Electrolyte 60 can be a solid polymer proton exchange membrane (PEM). Anexample of a solid polymer proton exchange membrane is a solid polymercontaining sulfonic acid groups. Such membranes are commerciallyavailable from E.I. DuPont de Nemours Company (Wilmington, Del.) underthe trademark NAFION. Alternatively, electrolyte 60 can also be preparedfrom the commercial product GORE-SELECT, available from W.L. Gore &Associates (Elkton, Md.). In some cases, electrolyte 60 can be apolyphosphazine membrane, or a membrane including an inorganic filler.In some embodiments, electrolyte 60 can be an ionically conductingliquid electrolyte (e.g., aqueous potassium hydroxide solution, aqueoussodium hydroxide solution, aqueous sulfuric acid solution, or aqueousphosphoric acid solution). The liquid electrolyte can be a free liquidor it can be immobilized by the addition of a gelling agent, such as apolymer (e.g., polyacrylic acid or polymethacrylic acid), or anabsorbing agent (e.g., silica gel, fumed silica, or clay).

Fuel cell housing 52 can be any conventional housing commonly used infuel cells. For example, housing 52 can be a plastic, carbon, or metalcontainer such as steel, stainless steel, graphite, nylon, polyvinylchloride, poly-tetrafluoroethylene, polyvinylidene fluoride,perfluoro-alkoxy resin, or a combination of metals, carbons, andplastics. Plastics may be filled, e.g., with mineral fillers.Alternatively, plastics may be unfilled. In some embodiments, the anodecan include a pressure control valve that can regulate the hydrogenpressure in the cell.

The generation of hydrogen from the generator is controlled bycontrolling delivery of the fluid (such as water or water includingdissolved catalyst) to the solid hydrogen source. More specifically, theinlet can be fluidly connected to a fluid control system configured tocontrol fluid flow rate to the solid hydrogen source. The fluid can bemechanically fed into the solid hydrogen source. Referring to FIG. 7A,generator 12 can include fluid control system 200, in which fluidcontainer 22 contains fluid chamber 202 and pressure chamber 204.Pressure chamber 204 is pre-pressurized with a gas, for example, aninert gas such as nitrogen, to a pressure P_(N2). The pressure P_(N2) inpressure chamber 204 is sufficient to transmit all of the fluid in fluidchamber 202 to the solid hydrogen source 18 through inlet 20 at apressure (P_(H2O)) higher than the internal pressure of the housing 12(P_(H2) _(—) _(IN)). A piston or diaphragm 206 moves in response to thepressure differential. A pressure actuated valve (P), which can be acomponent of inlet 20, serves to self-regulate the internal hydrogenpressure (P_(H2) _(—) _(IN)). A conformal buffer tank (BT) canaccommodate expansion of the solid hydrogen source and sudden loadchanges, which lead to faster hydrogen consumption from the generator.Hydrogen delivery pressure to the fuel cell (P_(H2) _(—) _(OUT)) isregulated to proper levels by a forward pressure regulator 210.

Referring to FIG. 7B, generator 12 can include fluid control system 200,in which fluid container 22 includes a piston or diaphragm 206 that isactuated by spring 208 to transfer the fluid to the solid hydrogensource 18. Spring 208 can be a compact belleville-washer stack with anon-linear force-displacement curve, which can deliver a relativelyconsistent force over the displacement range of the piston. A pressureactuated valve (P), which can be a component of inlet 20, serves toself-regulate the internal hydrogen pressure (P_(H2) _(—) _(IN)). Aconformal buffer tank (BT) can accommodate expansion of the solidhydrogen source and sudden load changes, which lead to faster hydrogenconsumption from the generator. The void space around the spring can beused as BT volume, decreasing wasted space. Hydrogen delivery pressureto the fuel cell (P_(H2) _(—) _(OUT)) is regulated to proper levels by aforward pressure regulator 210.

Referring to FIG. 7C, a gas-permeable membrane 32 at outlet 34 of thesolid hydrogen source 18 can contain materials within container 36.Material in solid hydrogen source 18 expands as hydrogen is produced andexits outlet 34. The expansion of the material can actuate piston ordiaphragm 206 toward fluid container 22, driving delivery of the fluidinto the solid hydrogen source. A pressure actuated valve (P), which canbe a component of inlet 20, serves to self-regulate the internalhydrogen pressure (P_(H2) _(—) _(IN)). A conformal buffer tank (BT) canaccommodate expansion of the solid hydrogen source and sudden loadchanges, which lead to faster hydrogen consumption from the generator.Hydrogen delivery pressure to the fuel cell (P_(H2) _(—) _(OUT)) isregulated to proper levels by a forward pressure regulator 210. A checkvalve 209 can be included adjacent to P to prevent back flow. Thisapproach can be more compact than systems that include mechanical movingparts.

In general, the hydrogen generator can be self-regulating, switching onand off in response to power demands. To accomplish self regulation,valve P can be configured as shown in FIGS. 8A and 8B. Referring to FIG.8A, as hydrogen is consumed, the hydrogen pressure in the generator(P_(H2) _(—) _(IN)) decreases and the valve 300 opens as piston 302 isactuated by spring 304 to initiate further hydrogen production byfluidly connecting the fluid container 22 and solid hydrogen source 18.Referring to FIG. 8B, an elastomeric diaphragm 306 can respond to thehydrogen pressure in the generator to open and close the fluidconnection between fluid container 22 and solid hydrogen source 18.Referring to FIG. 8C, pressure actuated valve P can be combined withoutlet pressure regulator 210 in an outlet pressure regulator/watercontrol valve 310. Valve 310 can regulate the hydrogen generatorpressure (P_(H2) _(—) _(IN)) down to a lower, steady value feeding intothe fuel cell (P_(H2) _(—) _(OUT)). Valve 310 is normally open and thusas hydrogen flows, pressure builds up downstream of the valve. As outletpressure (P_(H2) _(—) _(OUT)) increases, it is transferred to the valvethrough sensing orifice 312, which causes spring 314 to be compressed,eventually sealing at seat 319. As hydrogen is consumed and outletpressure drops, the force on the spring is reduced and the valve opensto let more hydrogen through. As hydrogen in the generator is depleted,P_(H2) _(—) _(IN) falls and the valve must open further to maintainP_(H2) _(—) _(OUT) at the desired level. When the valve opens almostcompletely, P_(H2) _(—) _(IN) is slightly greater that P_(H2) _(—)_(OUT), the inlet 20 is opened, allowing fluid to move from fluidcontainer 22 into solid hydrogen source 18 to generate more hydrogen.The output pressure can be set using knob 318. Because the forwardpressure regulator is a normally open valve, a separate on/off valve canbe used just before the fuel cell to seal off hydrogen pressure and flowduring periods of non-use. However, the pressure regulator will maintainthe working pressure in the lines upstream of the on/off valve, which isuseful for fast fuel cell start-up.

In an alternative approach, the solid hydride, preferably in acylindrical tablet form to minimize the void volume, can be dropped intothe water containing a catalyst to promote gas generation and thereaction efficiency. In this case, a runaway situation more easilyavoided since the maximum achievable hydrogen pressure is determined bythe tablet size. A stack of solid tablets can be stored in aspring-loaded compartment which can be actuated by a lowered hydrogenpressure to increase output.

Other embodiments are within the scope of the following claims.

1. A method of generating hydrogen comprising contacting a fluidincluding a proton source and a dissolved transition metal salt with asolid hydrogen source disposed within a housing having an outletconfigured to deliver the hydrogen to a hydrogen fuel cell.
 2. Themethod of claim 1, wherein contacting the fluid and the solid hydrogensource includes introducing the fluid into a hydrogen generator, thehydrogen generator comprising: the housing; the solid hydrogen source;and an inlet configured to guide the fluid to contact the solid hydrogensource.
 3. The method of claim 2, wherein the solid hydrogen sourceincludes a solid hydride.
 4. The method of claim 3, wherein the solidhydride is a pellet, tablet, cylinder, layer, or tube.
 5. The method ofclaim 3, wherein the solid hydride is sodium borohydride.
 6. The methodof claim 1, wherein the solid hydrogen source includes a solid hydridecombined with a wicking material.
 7. The method of claim 6, wherein thewicking material includes a hydrophilic material.
 8. The method of claim2, further comprising passing the fluid through the inlet to ahydrophilic material.
 9. The method of claim 1, further comprisingcontrolling the amount of fluid reaching the solid hydrogen source. 10.The method of claim 9, wherein controlling the amount of fluid reachingthe solid hydrogen source includes determining an amount of hydrogenexiting generator.
 11. The method of claim 9, wherein the fluid includeswater.
 12. The method of claim 11, wherein controlling the amount offluid reaching the solid hydrogen source includes delivering water vaporto the solid hydrogen source.
 13. The method of claim 1, wherein thetransition metal salt includes a ruthenium salt.
 14. The method of claim1, wherein the transition metal salt includes a cobalt salt.
 15. Themethod of claim 1, wherein the transition metal salt includes an ironsalt.
 16. The method of claim 1, wherein the transition metal saltincludes a transition metal chloride.
 17. The method of claim 1, whereinthe transition metal salt dissolves in the fluid as the fluid contactsor passes into the solid hydrogen source.
 18. The method of claim 17,wherein the solid hydrogen source includes a wicking material.
 19. Themethod of claim 18, wherein the transition metal salt is distributed on,dissolved in, or coated on the wicking material.
 20. The method of claim1, wherein the fluid comprises the dissolved transition metal saltbefore the fluid contacts the solid hydrogen source.